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Friday, May 13, 2011

NEW SuperSpeed USB 3.0

By Melissa J. Perenson, PCWorld
When you're in front of your PC, waiting for something to transfer to removable media, that's when seconds feel like minutes, and minutes feel like hours. And data storage scenarios such as that one is where the new SuperSpeed USB 3.0's greatest impact will be felt first. As of CES, 17 SuperSpeed USB 3.0-certified products were introduced, including host controllers, adapter cards, motherboards, and hard drives (but no other consumer electronics devices). Still more uncertified USB 3.0 products are on the way, and they can't get here fast enough.

Glance Backward

The beauty of USB 3.0 is its backward compatibility with USB 2.0; you need a new cable and new host adapter (or, one of the Asus or Gigabyte motherboards that supports USB 3.0) to achieve USB 3.0, but you can still use the device on a USB 2.0 port and achieve typical USB 2.0 performance. In reducing some overhead requirements of USB (now, the interface only transmits data to the link and device that need it, so devices can go into low power state when not needed), the new incarnation now uses one-third the power of USB 2.0.

The theoretical throughput improvement offered by USB 3.0 is dramatic -- a theoretical 10X jump over existing USB 2.0 hardware. USB 2.0 maxed out at a theoretical 480Mbps, while USB 3.0 can theoretically handle up to 5Gbps. Mind you, applications like storage will still be limited by the type of drive inside; so, for example, you can expect better performance from RAIDed hard drives or fast solid-state drives (SSDs) than from, say, a standalone single drive connected to the computer via USB 3.0.

The real-world examples are fairly convincing -- and underscore USB 3.0's advantage for high-def video, music, and digital imaging applications. Our early test results are encouraging as well: We tested Western Digital's My Book 3.0, the first USB 3.0-certified external hard drive. The performance was on a par with that of eSATA-but the benefit here is that USB 3.0 is a powered port, so you don't need to have another external power supply running to the drive (as you do with eSATA; unless the eSATA drive you're using is designed to steal power from a USB port while transferring data over the eSATA interface).

New Entries

While the WD drive was the first to announce, a slew of other hard drive makers either announced products at the show, or discussed plans to release products in the coming months. Among them: Seagate (which is doing a portable drive), LaCie, Rocstor, and Iomega. Even non-traditional hard drive vendors like Dane-Elec and A-Data showed products they billed as USB 3.0 (the latter two even had USB 3.0-connected SSDs, the first external drives to use solid-state storage inside.

One of the things to look for in the coming months is the certified SuperSpeed USB 3.0 logo. Products are currently filling the queues at the official certification testing labs, but presence of that certification logo will give you some peace of mind that the product you're buying truly does live up to the USB 3.0 spec.

Given that the certification labs are jammed up, though, you can expect companies to release USB 3.0 products without official certification. (Buffalo Technologies' drive, released late 2009, is not certified; LaCie's drives are in the process of certification, but will initially carry LaCie's own logo for USB 3.0, and will gain a sticker on the box once certification is completed.) And in those cases, it will be hard to know whether the device truly lives up to its performance potential.

Compatibility Guarantee

And this time around, the way the USB spec is written, says Jeff Ravencraft, consumers should have an easier time finding products that are truly USB 3.0. Before, in the transition from USB 1.1 to USB 2.0, the USB 2.0 spec was written in a way where it "encompassed low, full and high-speed USB," explains Ravencraft, president and chairman of the USB Implementers Forum. "Since those are all encapsulated in the USB 2.0 spec, [vendors] could have a certified product that's low-speed, but still call it USB 2.0.

"We don't have that issue with USB 3.0 To claim you're USB 3.0, you have to deliver 5Gbps. There's no other way to get the certification."

Ravencraft adds that the group is prepared to protect the USB 3.0 logo, to make sure that only manufacturers who go through certification use it. "We'll take legal action if anyone infringes on our marks."

By end of year, Ravencraft says the loggerjam of products awaiting certification should be past, and the organization's network of worldwide test labs will be handling USB 3.0 certification.

According to In-Stat Research, by 2013, more than one-quarter of USB 3.0 products will support SuperSpeed USB 3.0.

Ravencraft says this is the fastest ramp up of USB products he's seen in the past ten years, across the previous versions of USB.

I say the change can't come fast enough. The trick, though, will be getting the interface into our notebooks (without requiring a kludgy ExpressCard adapter). So far, though, only HP and Fujitsu have announced limited USB 3.0 support on notebooks. And Taiwanese notebook and desktop maker MSI indicated that it wouldn't have USB 3.0 until, at the earliest, the third-quarter of this year; product managers for both notebooks and desktops cited manufacturing concerns like chipset availability in large quantities, and the need to test USB 3.0 chipsets.

And in the meantime, the only announced peripherals remain storage devices. At next year's CES, it's likely we'll hear more about specific consumer electronics devices such as digital cameras and camcorders and video cameras moving to USB 3.0. Hopefully by then we'll start getting a critical mass of PC hardware with USB 3.0 integrated, too.


1. How does USB 3.0 achieve the extra performance?

USB 3.0 achieves the much higher performance by way of a number of technical changes. Perhaps the most obvious change is an additional physical bus that is added in parallel with the existing USB 2.0 bus. This means that where USB 2.0 previously had 4 wires (power, ground, and a pair for differential data), USB 3.0 adds 4 more for two pairs of differential signals (receive and transmit) for a combined total of 8 connections in the connectors and cabling. These extra two pairs were necessary to support the SuperSpeed USB target bandwidth requirements, because the two wire differential signals of USB 2.0 were not enough.
Furthermore, the signaling method, while still host-directed, is now asynchronous instead of polling. USB 3.0 utilizes a bi-directional data interface rather than USB 2.0's half-duplex arrangement, where data can only flow in one direction at a time. Without getting into any more technical mumbo jumbo, this all combines to give a ten-fold increase in theoretical bandwidth, and a welcome improvement noticeable by anyone when SuperSpeed USB products hit the market.

2. Isn't USB 2.0 fast enough?

Well, yes and no. USB 2.0 for many applications provides sufficient bandwidth for a variety of devices and hubs to be connected to one host computer. However, with today's ever increasing demands placed on data transfers with high-definition video content, terrabyte storage devices, high megapixel count digital cameras, and multi-gigabyte mobile phones and portable media players, 480Mbps is not really fast anymore. Furthermore, no USB 2.0 connection could ever come close to the 480Mbps theoretical maximum throughput, making data transfer at around 320 Mbps - the actual real-world maximum. Similarly, USB 3.0 connections will never achieve 4.8Gbps, but even 50% of that in practice is almost a 10x improvement over USB 2.0.

3. What other improvements does USB 3.0 provide?

The enhancements to SuperSpeed USB are not just for higher data rates, but for improving the interaction between device and host computer. While the core architectural elements are inherited from before, several changes were made to support the dual bus arrangement, and several more are notable for how users can experience the improvement that USB 3.0 makes over USB 2.0:

More power when needed
50% more power is provided for unconfigured or suspended devices (150 mA up from 100 mA), and 80% more power is available for configured devices (900 mA up from 500 mA). This means that more power-hungry devices could be bus powered, and battery powered devices that previously charged using bus power could potentially charge more quickly.
A new Powered-B receptable is defined with two extra contacts that enable a devices to provide up to 1000 mA to another device, such as a Wireless USB adapter. This eliminates the need for a power supply to accompany the wireless adapter...coming just a bit closer to the ideal system of a wireless link without wires (not even for power). In regular wired USB connections to a host or hub, these 2 extra contacts are not used.

Less power when it's not needed
Power efficiency was a key objective in the move to USB 3.0. Some examples of more efficient use of power are:
Link level power management, which means either the host computer or the device can initiate a power savings state when idle
The ability for links to enter progressively lower power management states when the link partners are idle
Continuous device polling is eliminated
Broadcast packet transmission through hubs is eliminated
Device and individual function level suspend capabilities allow devices to remove power from all, or portions of their circuitry not in use

Streaming for bulk transfers is supported for faster performance
Isochronous transfers allows devices to enter low power link states between service intervals
Devices can communicate new information such as their latency tolerance to the host, which allows better power performance

To paint an accurate picture, not everything in USB 3.0 is a clear improvement. Cable length, for one, is expected to have a significant limitation when used in applications demanding the highest possible throughput. Although maximum cable length is not specified in the USB 3.0 specification, the electrical properties of the cable and signal quality limitations may limit the practical length to around 3 metres when multi-gigabit transfer rates are desired. This length, of course, can be extended through the use of hubs or signal extenders.
Additionally, some SuperSpeed USB hardware, such as hubs, may always be more expensive than their USB 2.0 counterparts. This is because by definition, a SuperSpeed hub contains 2 hubs: one that enumerates as a SuperSpeed hub, and a second one that enumerates as a regular high-speed hub. Until the USB hub silicon becomes an integrated SuperSpeed USB + Hi-Speed USB part, there may always be a significant price difference.

Some unofficial discussion has surfaced on the web with respect to fiber-optic cabling for longer cable length with USB 3.0. The specification makes no mention of optical cabling, so we conclude that this will be defined in a future spec revision, or left to 3rd party companies to implement cable extension solutions for SuperSpeed USB.

4. Will my existing peripherals still work? How will they co-exist?

The good news is that USB 3.0 has been carefully planned from the start to peacefully co-exist with USB 2.0. First of all, while USB 3.0 specifies new physical connections and thus new cables to take advantage of the higher speed capability of the new protocol, the connector itself remains the same rectangular shape with the four USB 2.0 contacts in the exact same location as before. Five new connections to carry receive and transitted data independently are present on USB 3.0 cables and only come into contact when mated with a proper SuperSpeed USB connection.

5. Where are those SuperSpeed USB 3.0 products?

USB 3.0 silicon such as USB host controllers, peripheral chipsets and hubs compliant with the SuperSpeed bus have arrived in the latter half of 2009. Since then, a handful of external hard drives, flash drives, storage docks, Blu-ray optical drives, high-end notebooks, and host adapters in both PCI Express and ExpressCard have begun appearing on retail shelves. Other companies have shown their plans to roll out solid-state drives and RAID. DisplayLink also revealed plans to ship USB 3.0-compliant USB video silicons by Q4 2010.

It is important to note that NEC (now Renesas Electronics) and Fresco Logic are the only fabs to produce xHCI USB 3.0 host silicons as of this writing (October 2010). Until Intel, nVidia and AMD start bundling USB 3.0 as part of their motherboard chipset, companies interested in equipping USB 3.0 on their systems will have to source from said fabs for the chipsets

The Colin Walls Blog

Although USB 2.0 has served us well for numerous applications for many years, the need for greater capacity, speed etc. drove the development of USB 3.0. In recent weeks, both AMD and Intel have announced USB 3.0 support in their chip-sets, so it follows that it will become commonplace in PC in the not too distant future. That implies that USB 3.0 peripherals will be in demand and, of course, they tend to be embedded systems …
The key benefit of USB 3.0 is speed. Along with the three speeds offered by USB 2.0 [Low Speed, Full Speed and High Speed], USB 3.0 adds SuperSpeed, which promises data transfer 10X faster than before. The other particularly noticeable benefit is bus power. It has become increasingly common to find devices that connect to a PC via USB and also draw all their power from the interface. For example, I have several external disk drives and a flatbed scanner that all afford me this convenience. With USB 3.0, the available power is almost doubled, which increases the scope for application of the facility.

The implementation of USB is somewhat complex, as the current USB wiring would not straightforwardly support higher speeds. USB 3.0 cables feature 4 extra wires to carry SuperSpeed data traffic, in addition to the 2 used by USB 2.0 for the other speeds. A single pair of wires is needed to send data. In addition to higher speed, SuperSpeed is bidirectional - data can go up and down the bus simultaneously - hence the 4 wires. Earlier USB implementations were all unidirectional. This change means that new cables and connectors are required. The good news is that there is reasonable backwards compatibility - older USB plugs can be accommodated by USB 3.0 sockets. Building a USB network using equipment that supports different versions is somewhat complex. For example, a USB 3.0 hub can only offer downstream SuperSpeed data transfer if there is unbroken support for SuperSpeed upstream to the host. Ultimately this is not a serious limitation.

Next week I will be at the Embedded Systems Conference in San Jose, California. I have a paper in the conference [which will actually be delivered by a very competent colleague] covering USB, with an emphasis on USB 3.0. I will also be hosting a Web seminar on the topic shortly. I strongly suspect that this will be a popular conference topic over the next year.

Your feedback is always welcome.
Thank you!

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